Sewage data shows traces of COVID-19 decreasing locally

ESCANABA — The amount of DNA from the virus responsible for COVID-19 detectable in Escanaba’s sewer water has dropped, falling to levels well below what could be seen as “average” for the area.

According to the Sentinel Wastewater Epidemiology Evaluation Project (SWEEP), the most recent sample submitted by the Escanaba Wastewater Plant, dated April 10, contained more viral DNA than only 9 percent of all samples submitted by the plant to SWEEP since the city began participating in the program in August of 2021.

The April 10 sample suggests a substantial drop in viral activity in the city. The sample immediately prior to it, dated for April 8, contained 16 percent more viral DNA than all other Escanaba samples. Prior to that, samples were in the 48th percentile and the 37th percentile on April 4 and April 1, respectively.

SWEEP also reports 15-day moving averages for communities that participate in the program, however these averages are structured into categories and not reported as hard numbers. As of April 13, the city was in the second most-significant category for viral decline, which is somewhere between a 100% and 999% drop in detectable viral DNA. The scale uses values above 100% for these values because it is designed to reflect the exponential growth seen by replicating viruses.

High and low viral detection correlates with increases and decreases in active cases of the disease, but it is impossible to know the number of active cases using sewer data alone. Even if testing is done perfectly, the amount of viral load varies within infected individuals and not all individuals infected with the virus are symptomatic.

At the start of the pandemic, this hole in the data was filled by the prevalence of tests performed by healthcare providers and at mobile testing sites, which were reported to the state. When home testing became the norm, the number reported by health officials became less and less reliable as fewer positive infections were included in the data.

Still, the Michigan Department of Health and Human Services (MDHHS) reports the number of new cases reported in each county statewide that result from tests performed in a healthcare setting. These cases may be part of routine testing procedures, such as before routine surgeries, or may be the result of an individual who is ill and seeking treatment.

According to MDHHS, the number of new infections has also fallen U.P.-wide. The most recent MDHHS case data from the week of April 13 is shown below.

Gogebic – 5

Ontonagon – 0

Houghton – 4

Keweenaw – 0

Iron – 1

Baraga – 0

Dickinson – 1

Marquette – 4

Menominee – 6

Delta – 2

Alger – 0

Schoolcraft – 0

Luce – 3

Mackinac – 0

Chippewa – 2

It is important to note that the number of cases reported by MDHHS is the number of new cases. Cases that were identified in the prior week but are still active are not reported in the data.

No new deaths related to the virus were reported in the U.P. for the week of April 13 by MDHHS. Statewide only 810 new cases of the virus were reported, and there were six deaths.


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